NANOSCALEMATERIALS INCHEMISTRY

Second Edition

Kenneth J. Klabunde and Ryan M. Richards

Edited by

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NANOSCALEMATERIALS INCHEMISTRY

NANOSCALEMATERIALS INCHEMISTRY

Second Edition

Kenneth J. Klabunde and Ryan M. Richards

Edited by

Copyright # 2009 by John Wiley & Sons, Inc. All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New JerseyPublished simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:

Nanoscale materials in chemistry.—2nd ed. / [edited by] Kenneth J. Klabunde andRyan M. Richards.

p. cm.Includes index.ISBN 978-0-470-22270-6 (cloth)

1. Nanostructured materials. I. Klabunde, Kenneth J. II. Richards, Ryan.TA418.9.N35N345 2009660—dc22

2008053437

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

http://www.copyright.comhttp://www.wiley.com/go/permissionhttp://www.wiley.com

To Sarah, Sydney, Maya, Erik,and Tyler

CONTENTS

CONTRIBUTORS xi

PART I INTRODUCTION TO NANOMATERIALS 1

1 Introduction to Nanoscale Materials in Chemistry, Edition II 3Ryan M. Richards

2 Unique Bonding in Nanoparticles and Powders 15Keith P. McKenna

3 Particles as Molecules 37C. M. Sorensen

PART II NEW SYNTHETIC METHODS FOR NANOMATERIALS 71

4 Microwave Preparation of Metal Fluorides andtheir Biological Application 73David S. Jacob, Jonathan Lellouche, Ehud Banin, and Aharon Gedanken

5 Transition Metal Nitrides and Carbides 111Piotr Krawiec and Stefan Kaskel

vii

6 Kinetics of Colloidal Chemical Synthesis of MonodisperseSpherical Nanocrystals 127Soon Gu Kwon and Taeghwan Hyeon

7 Nanorods 155P. Jeevanandam

PART III NANOSTRUCTURED SOLIDS: MICRO- ANDMESOPOROUS MATERIALS AND POLYMERNANOCOMPOSITES 207

8 Aerogels: Disordered, Porous Nanostructures 209Stephanie L. Brock

9 Ordered Microporous and Mesoporous Materials 243Freddy Kleitz

10 Applications of Microporous and Mesoporous Materials 331Anirban Ghosh, Edgar Jordan, and Daniel F. Shantz

PART IV ORGANIZED TWO- AND THREE-DIMENSIONALNANOCRYSTALS 367

11 Inorganic–Organic Composites 369Warren T. Ford

12 DNA-Modified Nanoparticles: Gold and Silver 405Abigail K. R. Lytton-Jean and Jae-Seung Lee

PART V NANOTUBES, RIBBONS, AND SHEETS 441

13 Carbon Nanotubes and Related Structures 443Daniel E. Resasco

PART VI NANOCATALYSTS, SORBENTS, ANDENERGY APPLICATIONS 493

14 Reaction of Nanoparticles with Gases 495Ken-Ichi Aika

15 Nanomaterials in Energy Storage Systems 519Winny Dong and Bruce Dunn

CONTENTSviii

PART VII UNIQUE PHYSICAL PROPERTIESOF NANOMATERIALS 537

16 Optical and Electronic Properties of Metal andSemiconductor Nanostructures 539Mausam Kalita, Matthew T. Basel, Katharine Janik, and Stefan H. Bossmann

PART VIII PHOTOCHEMISTRY OF NANOMATERIALS 579

17 Photocatalytic Purification of Water and Air overNanoparticulate TiO2 581Igor N. Martyanov and Kenneth J. Klabunde

18 Photofunctional Zeolites and Mesoporous MaterialsIncorporating Single-Site Heterogeneous Catalysts 605Masakazu Anpo, Masaya Matsuoka, and Masato Takeuchi

19 Photocatalytic Remediation 629Shalini Rodrigues

PART IX BIOLOGICAL AND ENVIRONMENTAL ASPECTSOF NANOMATERIALS 647

20 Nanomaterials for Environmental Remediation 649Angela Iseli, HaiDoo Kwen, and Shyamala Rajagopalan

21 Nanoscience and Nanotechnology: Environmental andHealth Impacts 681Sherrie Elzey, Russell G. Larsen, Courtney Howe, and Vicki H. Grassian

22 Toxicity of Inhaled Nanomaterials 729John A. Pickrell, L. E. Erickson, K. Dhakal, and Kenneth J. Klabunde

INDEX 771

CONTENTS ix

CONTRIBUTORS

Ken-Ichi Aika, The Open University of Japan, Setagaya-ku, Tokyo, Japan

Masakazu Anpo, Department of Applied Chemistry, Graduate School ofEngineering, Osaka Prefecture University, Osaka 599-8531, Japan

Ehud Banin, The Institute for Advanced Materials and Nanotechnology, Bar-IlanUniversity, Ramat-Gan 52900, Israel

Matthew T. Basel, Kansas State University, Department of Chemistry andTerry C. Johnson Center for Basic Cancer Research, Manhattan, Kansas

Stefan H. Bossmann, Kansas State University, Department of Chemistry andTerry C. Johnson Center for Basic Cancer Research, Manhattan, Kansas

Stephanie L. Brock, Department of Chemistry, Wayne State University, Detroit,Michigan

K. Dhakal, Comparative Toxicology Laboratories, Department of DiagnosticMedicine/Pathobiology, Kansas State University, Manhattan, Kansas

Winny Dong, Chemical and Materials Engineering, California State PolytechnicUniversity, Pamona, California

Bruce Dunn, Department of Materials Science and Engineering, University ofCalifornia, Los Angeles, Los Angeles, California

Sherrie Elzey, Department of Chemical and Biochemical Engineering, Universityof Iowa, Iowa City, Iowa

xi

L.E. Erickson, Department of Chemical Engineering, Kansas State University,Manhattan, Kansas

Warren T. Ford, Department of Chemistry, Oklahoma State University, Stillwater,Oklahoma

Aharon Gedanken, Department of Chemistry, Kanbar Laboratory for Nano-materials, Nanotechnology Research Center, Bar-Ilan University, Ramat-Gan52900, Israel

Anirban Ghosh, Artie McFerrin Department of Chemical Engineering, Texas A&MUniversity, College Station, Texas

Vicki H. Grassian, Departments of Chemical and Biochemical Engineering andChemistry and the Nanoscience and Nanotechnology Institute at the Universityof Iowa, Iowa City, Iowa

Courtney Howe, Department of Nanoscience and Nanotechnology Institute at theUniversity of Iowa, Iowa City, Iowa

Taeghwan Hyeon, National Creative Research Initiative Center for OxideNanocrystalline Materials, and School of Chemical and Biological Engineering,Seoul National University, Seoul 151-744, Korea

Angela Iseli, NanoScale Corporation, Manhattan, Kansas

David S. Jacob, Department of Chemistry, Kanbar Laboratory for Nanomaterials,Nanotechnology Research Center, Bar-Ilan University, Ramat-Gan 52900, Israel

Katharine Janik, Kansas State University, Department of Chemistry andTerry C. Johnson Center for Basic Cancer Research, Manhattan, Kansas

P. Jeevanandam, Department of Chemistry, Indian Institute of TechnologyRoorkee, Roorkee-247667, India

Edgar Jordan, Artie McFerrin Department of Chemical Engineering, Texas A&MUniversity, College Station, Texas

Mausam Kalita, Kansas State University, Department of Chemistry andTerry C. Johnson Center for Basic Cancer Research, Manhattan, Kansas

Stefan Kaskel, Institute of Inorganic Chemistry, Technical University of Dresden,Dresden, Germany

Kenneth J. Klabunde, Department of Chemistry, Kansas State University,Manhattan, Kansas

Freddy Kleitz, Canada Research Chair on Functional Nanostructured Materials,Department of Chemistry, Laval University, Québec, Canada

Piot Krawiec, Instituto de Tecnologı́a Quı́mica, UPV-CSIC, Valencia, Spain

HaiDoo Kwen, NanoScale Corporation, Manhattan, Kansas

CONTRIBUTORSxii

Soon Gu Kwon, National Creative Research Initiative Center for Oxide Nano-crystalline Materials, and School of Chemical and Biological Engineering, SeoulNational University, Seoul 151-744, Korea

Jonathan Lellouche, Department of Chemistry, Kanbar Laboratory for Nano-materials, Nanotechnology Research Center, Bar-Ilan University, Ramat-Gan52900, Israel

Russell G. Larsen, Departments of Chemistry and the Nanoscience andNanotechnology Institute at the University of Iowa, Iowa City, Iowa

Jae-Seung Lee, Massachusetts Institute of Technology, Cambridge, Massachusetts

Abigail K. R. Lytton-Jean, Massachusetts Institute of Technology, Cambridge,Massachusetts

Igor N. Martyanov, Department of Chemistry, University of Ottawa, Ottawa,Ontario, Canada

Masaya Matsuoka, Department of Applied Chemistry, Graduate School ofEngineering, Osaka Prefecture University, Osaka, 599-8531, Japan

Keith P. McKenna, London Centre for Nanotechnology and University CollegeLondon, London, UK

John A. Pickrell, Comparative Toxicology Laboratories, Department of DiagnosticMedicine/Pathobiology, Kansas State University, Manhattan, Kansas

Shyamala Rajagopalan, NanoScale Corporation, Manhattan, Kansas

Daniel E. Resasco, School of Chemical, Biological, and Materials Engineering,University of Oklahoma, Norman, Oklahoma

Ryan M. Richards, Department of Chemistry and Geochemistry, Colorado Schoolof Mines, Golden, Colorado

Shalini Rodrigues, Macungie, Pennsylvania

Daniel F. Shantz, Artie McFerrin Department of Chemical Engineering, TexasA&M University, College Station, Texas

C. M. Sorensen, Department of Physics, Kansas State University, Manhattan,Kansas

Masato Takeuchi, Department of Applied Chemistry, Graduate School ofEngineering, Osaka Prefecture University, Osaka, 599-8531, Japan

CONTRIBUTORS xiii

PART I

INTRODUCTION TONANOMATERIALS

1INTRODUCTION TO NANOSCALEMATERIALS IN CHEMISTRY,EDITION II

RYAN M. RICHARDS

1.1 Introduction, 4

1.2 Systems with Delocalized Electrons, 4

1.3 Systems with Localized Electrons, 6

1.4 Instrumentation Introduction, 8

1.5 Conclusion, 9

Problems, 9

Answers, 10

Nanoscale Materials in Chemistry covers a broad area of science and engineeringat the core of future technological development. In particular, the challenges ofenergy and sustainability are certain to be interrelated with breakthroughs in thisarea. Among current buzz words (i.e. green, bio-, eco-), “nano” has been used (andabused) to describe an amazingly broad spectrum of systems that has led to frustrationfor many scientists. The National Nanotechnology Initiative has defined nanotech-nology as “working at the atomic, molecular and supramolecular levels, in thelength scale of approximately 1–100 nm range, in order to understand and creatematerials, devices and systems with fundamentally new properties and functionsbecause of their small structure” (www.nano.gov). Naturally, this broadly definedarea of science and engineering has a significant “chemistry” component. This bookaims to explore the chemistry, both traditional and emerging, that is associated withnanoscale materials.

Nanoscale Materials in Chemistry, Second Edition. Edited by K. J. Klabunde and R. M. RichardsCopyright # 2009 John Wiley & Sons, Inc.

3

This book is intended to function as both a teaching text for upper-levelundergraduate or graduate courses and a reference text, and both fundamentaland applied aspects of this field are covered in the chapters. It is intended that eachchapter be able to stand on its own to allow instructors to select those topics mostappropriate for their course. Additionally, each chapter contains several problemsdesigned by the authors to challenge students and enhance their comprehension ofthe material.

In this short introduction, we introduce the field of nanoscience in a very generalsense and provide background that may be useful to readers not familiar withthis area. More in-depth discussions of each topic are provided in the individual chap-ters, but we have found that an initial superficial introduction to the most commonphenomena and instrumentation, followed by the problems provided at the end ofthe chapter, helps students to understand the broader picture and begin to explorethe literature.

1.1 INTRODUCTION

Nanoscience is the natural progression of science exploring the nature of matterbetween atoms and molecules (defined by quantum mechanics) and condensedmatter (defined by solid state chemistry/physics). Thus, one of the central questionsin nanoscience is “at what point in diminishing the size of a material does it beginto act more like an atom or molecule?” or, conversely, “how many atoms (in a cluster)does it take to begin observing bulk-like (solid state) behavior?”

With regard to nanoscale materials, there are three general classifications that can beused (at least for inorganics): (1) materials with delocalized electrons (metals orconductors), (2) materials with localized electrons (insulators) and (3) materialswith new structures (usually atomically defined) and properties (or new forms ofmatter) due to their nanostructure (C60 or carbon nanotubes). Semiconductors fallsomewhere in between classifications 1 and 2 depending on their band gap.Although these classes of materials will be discussed in detail in the chapters ofthis book, a quick review of general materials properties and the effects of reducingsize is provided here to give readers and students an opportunity to begin thinkingabout nanoscience in terms of atoms/molecules (i.e. chemistry).

1.2 SYSTEMS WITH DELOCALIZED ELECTRONS

One of the principal concepts influencing the chemistry and physical properties ofnanoscale materials with delocalized electrons is the quantum confinement effect.A metal can be thought of as a regular lattice of charged metal ions in a sea ofquasi-delocalized electrons. The most important property of metals is their ability totransport electrons. Electrons can become mobile only if the energy band they areassociated with is not fully occupied. If molecular orbital theory is used to generate

INTRODUCTION TO NANOSCALE MATERIALS IN CHEMISTRY, EDITION II4

the band structures, bulk metal possesses an indefinitely extended molecular orbital.The relationship between the molecular orbital of a finite molecular system and theindefinite situation in a bulk metal is that the highest occupied molecular orbital(HOMO) becomes the Fermi energy Ef of the free electron (Fig. 1.1). The Fermienergy depends only on the density of the electrons. If we assume that all levelsup to the Ef are occupied with a total of N electrons, it can be estimated that theaverage level spacing is d � Ef/N and therefore is inversely proportional to thevolume V ¼ L3 (L ¼ side length of particle) or d / Ef (lf/L)3 where lf ¼ wavelengthof an electron with Ef. The wave character of the electron is assumed here, includingthat the allowed values for the wavelength l are quantized (i.e. for an electron ina box of side L, only discreet values for the energy are allowed). The properties gen-erally associated with bulk metals require a minimum number of electronic levels ora band.

The electrons in a three-dimensional metal spread as waves of various wavelengthsusually called the DeBroglie wavelength.

l ¼ h=mv

where l ¼ electronic wavelength, h ¼ Planck’s constant, m ¼ mass of electron,and v ¼ speed of electron.

Delocalization of electrons in the conductivity band of a metal is possible as longas the dimension of the metal particle is a multiple of the DeBroglie wavelength.Thus, the smallest metal particles must have a dimension on the order of l. Smaller

Figure 1.1 Development of the band structure of a metal: (a) molecular state, (b) nanocluster,and (c) bulk with s and d bands. (From Schmid, G. Nanoscale Materials in Chemistry, ed. K.J. Klabunde. New York: Wiley, 2001.)

1.2 SYSTEMS WITH DELOCALIZED ELECTRONS 5

particles have electrons localized between atomic nuclei and behave more like mol-ecules. The transition between these two situations is gradual. Thus, for metals or sys-tems with delocalized electrons, upon decreasing size we ultimately reach a size wherethe band structure disappears and discreet energy levels occur and we have to applyquantummechanics; this is commonly referred to as the phenomenon of quantum con-finement. The quantization effect represents one of the most exciting areas of modernscience and has already found numerous applications in fields ranging from elec-tronics to biomedicine.

Quantization refers to the restriction of quasi-freely mobile electrons in a pieceof bulk metal and can be accomplished not only by reduction of the volume of abulk material but also by reducing the dimensionality. A quantum well refers to thesituation in which one dimension of the bulk material has been reduced to restrictthe free travel of electrons to only two dimensions. Restricting an additional dimen-sion then only allows the electrons to travel freely in one dimension and is called aquantum wire, while restricting all three dimensions results in a quantum dot.

1.3 SYSTEMS WITH LOCALIZED ELECTRONS

The effects of reducing size are very different for materials with localized electronswhere defects are the most significant contributor to their properties. Naturally, dueto the localization of electrons, the surface contains defects due to edges, corners,“f” centers, and other surface imperfections (Fig. 1.2). Defects can arise from a variety

Figure 1.2 A representation of the various defects present on metal oxides. (From Dyrek, K.and Che, M. Chem. Rev. 1997, 305–331. With permission.)

INTRODUCTION TO NANOSCALE MATERIALS IN CHEMISTRY, EDITION II6

of causes: they may be thermally generated, or may arise in the course of fabrication ofthe solid, incorporated either unintentionally or deliberately. Defects are importantbecause they are much more abundant at surfaces than in bulk, and in nanoscalematerials they become predominant due to the large surface area (Fig. 1.3). Becauseof the number of atoms at the surface and the limited number of atoms within thelattice, the chemistry and bonding of nanoparticles is greatly affected by the defectsites present.

The defects that occur in the solids with localized electrons are grouped intothe following classes: point, linear, planar, and volumetric defects. Point defects area result of the absence of one of the constituent atoms (or ions) on the lattice sites,or their presence in interstitial positions. The most common defects are coordinativelyunsaturated sites, for example, materials with a rock salt structure prefer to be boundto six neighbors, so those atoms on the surface are five-coordinate, on edges four-coordinate, and corners three-coordinate. Thus, using MgO as an example, thecoordinatively unsaturated sites possess Lewis base character. Further, the crystallo-graphic facet on the surface (as given by Miller indices) can also dramaticallyinfluence the properties of the system. For example, the (100) facet of MgO consistsof alternating Mg cations and O anions and is thermodynamically favored, however,the (111) facet consisting of alternating layers of cations and anions has a polar surfaceand therefore different physical and chemical properties (Fig. 1.4).

Figure 1.3 Calculated surface to bulk atomic ratio (for Fe). (From K. J. Klabunde et al.J. Phys. Chem. 1996, 100: 12142–12153. With permission.)

1.3 SYSTEMS WITH LOCALIZED ELECTRONS 7

1.4 INSTRUMENTATION INTRODUCTION

Developments in instrumentation, in particular microscopy, have allowed scientiststo observe materials and phenomena with angstrom-level resolution, leading toa much deeper understanding of nanostructured materials. The two types of electronmicroscopy, scanning electron microscopy (SEM) and transmission electronmicroscopy (TEM), utilize an electron beam rather than light to resolve images(Fig. 1.5). In general, a TEM can be envisioned as a process similar to a film projectorin which a beam passes through a sample and projects an image onto a screen.Conversely, an SEM is more comparable to shining a flashlight around a room andgaining a sense of the topography. With this technique resolution limits are generallyon the nanometer length scale but the advantage lies in the topographical informationgained. A great deal of caution should be taken when assessing the data providedby these techniques because they are operator biased in that they only show a smallportion of the overall sample. While electron microscopy images provide valuableinformation regarding size, shape, composition, etc., they should be corroboratedby a “bulk” technique such as powder x-ray diffraction (XRD) to demonstrate thatthe information in the microscopy image is representative of the whole sample.

In addition to electron microscopy techniques, developments in scanning probemicroscopies have also allowed visualization and even the ability to manipulatematter at a new level. This class of microscopies acquires data by using a physical

Figure 1.4 Schematic depiction of the (100), (110), and (111) facets of MgO.

INTRODUCTION TO NANOSCALE MATERIALS IN CHEMISTRY, EDITION II8

probe to scan the surface (Fig. 1.5). Generally, the probe is moved mechanically acrossthe surface in a raster scan, providing line by line data of the probe location andthe interaction with the surface. There are now countless types of scanning probemicroscopies, with the two most common being atomic force microscopy (AFM)and scanning tunneling microscopy (STM).

1.5 CONCLUSION

Hopefully, this short introduction instigates some class discussion about nanoscalematerials in chemistry and facilitates an entry into the topics covered in this bookand the literature. The editors have attempted to gather chapters covering a breadthof topics both fundamental and applied to provide the reader with an understandingof this important area of science and engineering. The contributors have been selectedfor their expertise in the subject area and have all done an excellent job of sharingtheir knowledge and making their topic accessible to a broad readership.

PROBLEMS

1. Draw figures illustrating the relationship of the density of states versus energy for(a) bulk, (b) quantum well, (c) quantum wire, and (d) quantum dots.

2. For a 2.1 nm cube of MgO (100) calculate the number of five-, four-, and three-coordinate sites.

Figure 1.5 Schematic depiction of traditional light microscopy, transmission electronmicroscopy, scanning electron microscopy, and scanning probe microscopy.

PROBLEMS 9

3. Use the magic numbers equation S(10n2 þ 2) to show the number of atoms inclusters with one, two, and three shells and calculate the number of surfaceatoms in each.

4. List five types of scanning probemicroscopies and give a brief description of each.

5. Find the 12 principles of Green Chemistry and discuss how nanotechnologymight have an impact on these areas.

6. Investigate the following analytical techniques and provide a brief description ofeach, including the information provided and limitations: TEM, SEM, powderXRD, XPS, EXAFS, XANES, nitrogen physisorption.

7. Explain what happens to the melting point and specific heat of metals as the sizechanges from the bulk to the nanoscale.

8. Provide MO diagrams for Li2, Li20, and bulk Li.

9. Describe what is meant by “bottom up” and “top down” preparations of nanoscalematerials.

10. Describe the two paradigms of colloidal stabilization, steric and electrostatic, andprovide an example of each.

ANSWERS

1. From K. J. Klabunde, editor. Nanoscale Materials in Chemistry, 1st edn.New York: Wiley Interscience, 2001, p. 22.

2. For MgO 100, d spacing is �2.1 Å, thus a 2.1nm cube is �10 � 10 � 10 unitsor 1000 MgO that break down as follows:

5 coordinate ¼ faces ¼ 8 � 8 � 6 (# faces)

INTRODUCTION TO NANOSCALE MATERIALS IN CHEMISTRY, EDITION II10

4 coordinate ¼ edges ¼ 8 � 12 (# edges)3 coordinate ¼ corners ¼ 8leaving a core of 8 � 8 � 8Note: some students have an easier time starting with corners, then edges andfaces. Also, this is a simplified exercise, in reality the highly unsaturated sitesare often hydroxylated and the overall charge of the molecule is balanced.

3. 1 shell ¼ 13 atoms (12 on surface)2 shells ¼ 55 atoms (42 on surface)3 shells ¼ 147 atoms (92 on surface)

4. Any of the following surface probe microscopies are possible:AFM, atomic force microscopy

Contact AFMNon-contact AFMDynamic contact AFMTapping AFM

BEEM, ballistic electron emission microscopy

EFM, electrostatic force microscope

ESTM, electrochemical scanning tunneling microscope

FMM, force modulation microscopy

KPFM, kelvin probe force microscopy

MFM, magnetic force microscopy

MRFM, magnetic resonance force microscopy

NSOM, near-field scanning optical microscopy (or SNOM, scanning near-fieldoptical microscopy)

PFM, piezo force microscopy

PSTM, photon scanning tunneling microscopy

PTMS, photothermal microspectroscopy/microscopy

SAP, scanning atom probe

SECM, scanning electrochemical microscopy

SCM, scanning capacitance microscopy

SGM, scanning gate microscopy

SICM, scanning ion-conductance microscopy

SPSM, spin polarized scanning tunneling microscopy

SThM, scanning thermal microscopy

STM, scanning tunneling microscopy

SVM, scanning voltage microscopy

SHPM, scanning Hall probe microscopy

Of these techniques AFM and STM are the most commonly used followed byMFM and SNOM/NSOM.

ANSWERS 11

5. The 12 principles of Green Chemistry:This is a rapidly developing area of science and instructors may find it helpful touse recent literature reports to illustrate these points.

(1) Prevention: It is better to prevent waste than to treat or clean up waste after ithas been created. (Catalysis by nanoscale particles.)

(2) Atom Economy: Synthetic methods should be designed to maximize theincorporation of all materials used in the process into the final product.(Optimizing the number of surface atoms and their activity comes frommaking nanoscale materials.)

(3) Less Hazardous Chemical Syntheses: Wherever practicable, syntheticmethods should be designed to use and generate substances that possesslittle or no toxicity to human health and the environment. (There havebeen several reports of nanoscale catalysts that have allowed processesto become more green, using water as solvent or no solvents, eliminate byproducts, etc.)

(4) Designing Safer Chemicals: Chemical products should be designed toeffect their desired function while minimizing their toxicity. (Nanotoxicityand nanoparticle lifecycle in the environment needs to be closely studied.)

(5) Safer Solvents and Auxiliaries: The use of auxiliary substances when used.

(6) Design for Energy Efficiency: Energy requirements of chemical processesshould be recognized for their environmental and economic impacts andshould be minimized. If possible, synthetic methods should be conductedat ambient temperature and pressure. (Nanocatalysis.)

(7) Use of Renewable Feedstocks: A raw material or feedstock should berenewable rather than depleting whenever technically and economicallypracticable.

(8) Reduce Derivatives: Unnecessary derivatization (use of blocking groups,protection/deprotection, temporary modification of physical/chemicalprocesses) should be minimized or avoided if possible, because suchsteps require additional reagents and can generate waste.

(9) Catalysis: Catalytic reagents (as selective as possible) are superior to stoi-chiometric reagents. (Many nanoscale catalysts exhibit improved selectivityand/or activity as compared to bulk systems.)

(10) Design for Degradation: Chemical products should be designed so that atthe end of their function they break down into innocuous degradationproducts and do not persist in the environment.

(11) Real-time Analysis for Pollution Prevention: Analytical methodologiesneed to be further developed to allow for real-time, in-process monitoringand control prior to the formation of hazardous substances.

(12) Inherently Safer Chemistry for Accident Prevention: Substances and theform of a substance used in a chemical process should be chosen to mini-mize the potential for chemical accidents, including releases, explosions,and fires.

INTRODUCTION TO NANOSCALE MATERIALS IN CHEMISTRY, EDITION II12

From P. T. Anastas, J. C. Warner. Green Chemistry: Theory and Practice.New York: Oxford University Press, 1998, p. 30. By permission of OxfordUniversity Press.

6. TEM: Under vacuum conditions focuses an electron beam through a sample dis-persed on a grid. The resulting image can provide Å level resolution includinglattice fringes. Most useful for determining particle size, size distribution andshape. Can also provide a great deal of additional information from diffractiontechniques.

SEM: Provides more topography information than TEM but resolution isgenerally limited to nm scale.

Powder XRD: Provides information regarding unit cell, long range order, bond-ing and lattice. Can be helpful to determine the phase of a material (forexample anatase vs rutile for TiO2) and Scherrer eqn can be applied to estimateparticle size.

XPS, X-ray photoelectron spectroscopy: Can be used to study first few layers ofsurface and provide the energies of the orbitals. This information can then beused to determine oxidation state of the element.

EXAFS and XANES are generally performed at a synchotron facility and provideinformation about neighboring atoms of the atom under investigation.

Nitrogen physisorption: Used to determine surface area, pore size, pore volume,pore size distribution and further textural properties through analysis ofadsorption/desorption isotherms.

7. Students are directed to Chapter 8 in the first edition for comprehensive discussion.(See K. J. Klabunde, editor. Nanoscale Materials in Chemistry, 1st edn. NewYork: Wiley Interscience, 2001, pp. 263–277). In general, for free nanoparticlesthe melting point is always lower than the bulk value. Specific heats are generallyenhanced as compared to the bulk.

8. From K. J. Klabunde, editor. Nanoscale Materials in Chemistry, 1st edn. NewYork: Wiley Interscience, 2001, p. 16.

ANSWERS 13

9. “Top down” approaches to nano refer to those in which larger systems arebroken down until they reach they nanoscale while “bottom up” involves buildingnanoscale materials by putting together atoms or molecules.

10. The two general modes of colloidal stabilization are electrostatic (left) and steric(right). In the electrostatic mode there is a bilayer of anions (often halides) and asecond layer of cations (for example tetra alkylammonium). In the steric stabiliz-ation there is a single bulky molecule attached to the surface (usually a P, N, or Sdonor, alkyl thiols are common).

INTRODUCTION TO NANOSCALE MATERIALS IN CHEMISTRY, EDITION II14